1. Field of the Invention
The invention relates to face detection and recognition, particularly under out of focus conditions.
2. Description of the Related Art
Viola-Jones proposes a classifier chain consisting of a series of sequential feature detectors. The classifier chain rejects image patterns that do not represent faces and accepts image patterns that do represent faces.
A problem in face recognition processes arises when faces that are out of focus are distributed in a large area of face space making correct classification difficult. Faces with similar focus conditions tend to be clustered together and correct clustering of images of the same person is difficult. It is desired to be able to detect faces that are out of focus within images, or where another difficult characteristic of a face exists such as a face having a non-frontal pose or uneven illumination. It is also desired to have a method to normalize focus on faces, for example, for use in face recognition and/or other face-based applications.
Each of Mitra S et al “Gaussian Mixture Models Based on the Frequency Spectra for Human Identification and Illumination Classification”, 4th IEEE Workshop on Automatic Identification Advanced Technologies, 2005, Buffalo, N.Y., USA 17-18 Oct. 2005, pages 245-250; and Kouzani A Z “Illumination-effects compensation in facial images”, IEEE International Conference on Systems, Man, and Cybernetics, 1999, IEEE SMS '99 Conference Proceedings, Tokyo, Japan 12-15 Oct. 1999, vol 6 pages 840-844 disclose conventional face illumination normalization methods.
Having objects at different distances to a digital camera, or a camera-phone, video camera, or other camera-enabled device or image acquisition device, in focus is a well known problem in the digital photography industry. Solutions such as extended depth of field do tackle this problem, but only partially, ensuring that the close objects are still sharp when the camera focuses to infinity (deep focus). It is desired to have an efficient technique to handle digital images initially having out of focus objects.